CH. II.] LABORATORY MICROSCOPES. 63 



FIGURES OF LABORATORY MICROSCOPES AND 

 ACCESSORY APPARATUS. 



It was deemed advisable in this new edition to figure some of the 

 most common of the laboratory microscopes and this has been rendered 

 possible mostly by the courtesy of the makers and importers. During 

 the last five years very great vigor has been shown in the microscopical 

 world. This has been stimulated largely by the activity in biological 

 science and the widespread appreciation of the microscope, not only as 

 a desirable, but as a necessary instrument of study and research. The 

 production of the new kinds of glass (Jena glass) , and the apochromatic 

 objectives have been a no less potent factor in promoting progress. It 

 is gratifying also to know that with the increase in the use of the mi- 

 croscope, not only are the optical and mechanical parts improved, and 

 that very greatly, but the price has decreased so that at the present time 

 schools cannot afford to be without one or more, and individuals are not 

 debarred from the possession of an instrument adequate to their needs. 

 The cost of a complete outfit varies from 25 to 600 dollars. The stu- 

 dent is advised to write to one or. more of the opticians for complete 

 catalogs. See list, p. 2 of cover. 



\ ilS. Marker lor Preparations. ( Figs. 61-66). — This instrument consists of an 

 objective-like attachment which may be screwed into the nose-piece of the micro- 

 scope. It bears on its lower end (Figs. 61-3) a small brush and the brush can be 

 made more or less eccentric and can be rotated, thus making a larger or smaller 

 circle. In using the marker the brush is dipped in colored shellac or other cement 

 and when the part of the preparation to be marked is found and put exactly in the 

 middle of the field the objective is turned aside and the marker turned into posi- 

 tion. The brush is brought carefully in contact with the cover- glass and rotated. 

 This will make a delicate ring of the colored cement around the object. Within 

 this very small area the desired object can be easily found on any microscope. 

 The brush of the marker should be cleaned with 95 % alcohol after it is used. 

 (Proc. Anier, Micr. Soc, 1894, pp. 112-11S). 



\ 119. Pointer in the Ocular. — The Germans have a pointer ocular (Spitzen- 

 Okular), an ocular with one or two delicate rods or pointers at the level of the 

 real image, that is, at the level of the diaphragm (Figs. 21, 30 D). For the 

 purposes of demonstrating any particular structure or object in the field, a tempo- 

 rary pointer may be easily inserted in any ocular as follows : Remove the eye-lens 

 and with a little mucilage or Canada balsam fasten an eyelash (cilium) to the 

 diaphragm (Fig. 30 D) so that it will project about half way across the opening. 

 If one uses this ocular, the pointer will appear in the field and one can place the 

 specimen so that the pointer indicates it exactly, as in using a pointer on a diagram 

 or on the black-board. It is not known to the author who devised this method. 

 It is certainly of the greatest advantage in demonstrating objects like arnoebas or 

 white blooJ corpuscles to persons not familiar with them, as the field is liable to 



